DBA is caused by a mutation (error) in a gene that codes for producing red blood cells from stem cells (blood-forming cells produced by the bone marrow). In 5 to 10 years, gene transfer therapy may prove to be an effective treatment for DBA. Before this treatment can be considered, however, more information is needed about DBA patients and how their stem cells function. This study will examine: 1) whether stem cells of patients with DBA respond to G-CSF the same way those of healthy people do. (G-CSF is a drug that causes stem cells to move from the bone marrow to the blood stream, where they can be collected more easily and in larger numbers by a procedure called leukapheresis, described below. If G-CSF does not work well in DBA patients, other collection strategies will have to be explored); and 2) whether the genetic error in DBA can be corrected by gene transfer into patients' stem cells.